Paper feeder and image forming device incorporating same

ABSTRACT

A paper feeder including: a push-up mechanism that pushes up an end portion of a tray below a leading end of a stack of sheets; a paper feed roller that intersects a locus fitted to motion of the end portion of the tray or an extension of the locus in the direction of the motion, and applies a conveying force to a sheet that the push-up mechanism presses against the paper feed roller to move the sheet in a conveyance direction; a separation member that forms a nip with the paper feed roller and applies a resistance force in a direction opposite the conveyance direction to the sheet; and an auxiliary roller upstream in the conveyance direction from the locus that applies a conveying force in the conveyance direction to the sheet, maintaining a state of contact between the sheet and the paper feed roller.

This application claims priority to Japanese Patent Application No. 2018-70636, filed Apr. 2, 2018, the contents of which are hereby incorporated herein by reference in their entirety.

BACKGROUND Technical Field

The present disclosure relates to paper feeders, and in particular to paper feeders incorporating a mechanism that pushes up sheets stacked on a tray.

Description of the Related Art

“Paper feeder” indicates a device that automatically feeds a sheet to a machine that processes the sheet, such as a printer, copier, scanner, facsimile machine, finisher, or the like. A paper feeder generally includes a paper feed cassette, a pickup roller, and a pair of a paper feed roller and a separation member (for examples, see JP H5-294484 and JP 2014-058400). A stack of sheets can be stacked in the paper feed cassette. The pickup roller is installed above the paper feed cassette and rotates while its outer circumferential surface is pressed against a top surface of the sheet stack. The frictional force generated (=coefficient of friction between sheet surface and outer circumferential surface×pressure applied to sheet surface; hereinafter referred to as “conveying force”) moves a sheet from the top surface of the sheet stack. At the destination of this movement the paper feed roller forms a nip with the separation member. The paper feed roller applies a conveying force to a front surface of a sheet reaching the nip. The separation member is a pad or roller, and applies to a back surface of the sheet passing through the nip a friction force in the opposite direction of the direction of the conveying force. Even if a second sheet is fed along with the first sheet (multi-feed), the second sheet is prevented from proceeding by the friction force from the separation member, and separated from the first sheet. In this way, the paper feeder feeds sheets separately, one at a time, from the sheet stack.

The mechanism of using the pickup roller to pick up the sheet from the paper feed cassette and feed the sheet to the nip between the paper feed roller and the separation member is effective in reliably separating the sheet from the sheet stack. However, in order that the pickup roller can reliably pick up the sheet regardless of sheet size, the pickup roller must be separated to some extent from the nip between the paper feed roller and the separation member. This means that a sufficiently large space to install the pickup roller needs to be secured above the paper feed cassette, which is disadvantageous for miniaturization of the paper feeder. In particular, when said mechanism is adopted for a manual feed tray that can be stored in a main body of a device, a storage location of the pickup roller needs to be secured in the main body for when the manual feed tray is stored, and this is difficult to reconcile with device miniaturization.

For the purpose of solving this difficulty, paper feeders have been developed in which the pickup roller is omitted, and in accordance with loading of sheets into the paper feed cassette, a leading end of the sheets is brought into direct contact with the outer circumferential surface of the paper feed roller (for examples, see JP 2013-155036 and JP 2014-040312). This type of paper feeder typically has a push-up mechanism for pushing up at least part of a sheet stacking area (hereinafter also referred to as a tray) in the paper feed cassette. The push-up mechanism presses, via the tray, the leading end of a topmost sheet of the sheets on the tray against the outer circumferential surface of the paper feed roller, the sheet thereby being drawn into the nip between the paper feed roller and the separation member by the conveying force of the paper feed roller.

In a paper feeder that uses a pickup roller, a sheet in the paper feed cassette is first conveyed only by the pickup roller. Accordingly, the pickup roller typically requires a conveying force equivalent to that of the paper feed roller. Further, a certain distance exists from the leading end of the sheet to the nip between the paper feed roller and the separation member, and therefore there is a risk that the leading edge of the sheet deviates from the nip due to factors such as an externally received vibration shock while the sheet is moved this distance, or incorrect sheet state (bend, fold, orientation) prior to conveyance. If, in such a case, the pickup roller continues to apply the conveying force to the sheet, there is a risk of a paper jam at the nip between the paper feed roller and the separation member. In order to prevent such an occurrence, it is necessary to have, for example, a control to stop the pickup roller as soon as the leading end of the sheet deviates from the nip between the paper feed roller and the separation member. Such a control makes it difficult to achieve a low cost paper feeder, due to the requirement of a sensor, etc.

In a paper feeder that omits the pickup roller, the push-up mechanism of the tray must ensure that the leading end of the topmost sheet is pressed against the outer circumferential surface of the paper feed roller. However, for example, in a case where leading end positions of stacked sheets are excessively misaligned, or in a case where a friction force between the sheets is small and the leading end positions of the sheets deviate excessively from correct positions as the slope of the tray increases, deviation of the leading ends of the sheets from the outer circumferential surface of the paper feed roller may occur. Such sheets cannot be fed by the paper feeder unless a user manually adjusts them. Thus, it is difficult to further improve reliability of such paper feeders.

SUMMARY

An object of the present disclosure is to solve the technical problems mentioned above, and in particular to provide a paper feeder that can improve reliability of paper feeding without impeding the device miniaturization and cost reduction achievable by omission of the pickup roller.

To achieve at least one of the abovementioned objects, according to an aspect of the present disclosure, a paper feeder that feeds out a sheet from a stack of sheets stacked on a tray includes a push-up mechanism, a paper feed roller, a separation member, and an auxiliary roller. The push-up mechanism pushes up an end portion of the tray below a leading end of the stack. The paper feed roller includes an outer circumferential surface that intersects (i) a locus fitted to motion of an edge of the end portion of the tray when the push-up mechanism pushes up the end portion or (ii) an extension of the locus in the direction of the motion, the paper feed roller applying a conveying force to a sheet that the push-up mechanism presses against the outer circumferential surface of the paper feed roller via the end portion of the tray in order to move the sheet in a conveyance direction. The separation member forms a nip with the paper feed roller downstream in the conveyance direction from the locus, the separation member applying a resistance force in a direction opposite the conveyance direction to the sheet entering the nip due to the conveying force of the paper feed roller. The auxiliary roller includes an outer circumferential surface upstream in the conveyance direction from the locus, the auxiliary roller applying a conveying force in the conveyance direction to the sheet that the push-up mechanism presses against the outer circumferential surface of the auxiliary roller via the end portion of the tray, thereby maintaining a state of contact between the sheet and the outer circumferential surface of the paper feed roller.

BRIEF DESCRIPTION OF DRAWINGS

The advantages and features provided by one or more embodiments of the disclosure will become more fully understood from the detailed description given hereinbelow and the appended drawings which are given by way of illustration only, and thus are not intended as a definition of the limits of the invention. In the drawings:

FIG. 1 is a perspective view diagram illustrating appearance of an image forming device pertaining to an embodiment of the present disclosure.

FIG. 2 is a front view diagram schematically illustrating internal structure of a printer included in the image forming device illustrated in FIG. 1.

FIG. 3A is a perspective view diagram illustrating appearance of the paper feed cassette illustrated in FIG. 1; and FIG. 3B is a schematic diagram illustrating structure of a push-up mechanism relative to the tray illustrated in FIG. 3A.

FIG. 4A is a perspective view diagram illustrating appearance of the manual feed tray illustrated in FIG. 1; and FIG. 4B is an enlargement of an area around a central portion of an interior of a frame of the manual feed tray.

FIG. 5A and FIG. 5B are perspective view diagrams of a movable holder and a push-up plate illustrated in FIG. 4A, illustrated in retracted positions.

FIG. 6A and FIG. 6B are perspective view diagrams of the movable holder and the push-up plate illustrated in FIG. 4B, illustrated in pressure contact positions.

FIG. 7A is a frontal view diagram of the movable holder and the push-up plate in the retracted positions; and FIG. 7B is a frontal view diagram of the movable holder and the push-up plate in the pressure contact positions.

FIG. 8A and FIG. 8B are side view diagrams of a plunger of a solenoid, a link lever, and a projection of the movable holder illustrated in FIG. 6A and FIG. 6B; and FIG. 8C is a graph showing a relationship between a number of sheets passing through a nip between the paper feed roller and a separation roller illustrated in FIG. 5A and FIG. 5B and strength of a conveying force of an auxiliary roller.

FIG. 9A, FIG. 9B, and FIG. 9C illustrate a mechanism mounted inside a side pillar of the frame illustrated in FIG. 4A, where FIG. 9A is a perspective view diagram viewed at an angle from the front of the MFP illustrated in FIG. 1, FIG. 9B is a perspective view diagram viewed at an angle from the back of the MFP, and FIG. 9C is a back view diagram of the MFP.

FIG. 10 is a block diagram illustrating a structure of an electric control system of the printer illustrated in FIG. 2.

FIG. 11 is an example timing chart for signals transmitted from a control circuit of a feeder section illustrated in FIG. 9A, 9B, 9C to a drive circuit.

FIG. 12 is a front view diagram of a mechanism in a movable holder that uses a belt for torque transmission from a drive shaft 15S to a central shaft of an auxiliary roller 16X.

DETAILED DESCRIPTION

The following is a description of one or more embodiments of the present disclosure with reference to the drawings. However, the scope of the invention is not limited to the disclosed embodiments.

[Image Forming Device Appearance]

FIG. 1 is a perspective view diagram illustrating appearance of an image forming device pertaining to an embodiment of the present disclosure. The image forming device is a multi-function peripheral (MFP) 100 and has the functions of a scanner, a copier, and a printer. An auto document feeder (ADF) 110 is mounted on a top surface of a casing of the MFP 100, and is openable and closable. A scanner 120 is housed in an upper portion of the casing directly below the ADF 110, a printer 130 is housed in a lower portion of the casing, a paper feed cassette 11 is attached below the printer 130 and can be slid in and out from a front face of the casing, and a manual feed tray 16 is attached to a side face of the casing and can be opened vertically.

The MFP 100 is an in-body discharge type. That is, a discharge tray 44 is installed in a gap DSP between the scanner 120 and the printer 130, a discharge port (not visible in FIG. 1) is provided at one side of the gap DSP, and sheets are discharged from the discharge port to the discharge tray 44. An operation panel 51 is attached to a front-facing portion of the casing to one side of the gap DSP. A touch panel is embedded in a front face of the operation panel 51, around which are various mechanical push buttons. The touch panel displays a graphical user interface (GUI) screen such as an operation screen or input screen showing various information, and accepts user input operations through “widgets” such as an icon, a virtual button, a menu, a tool bar, or the like.

[Printer Structure]

FIG. 2 is a front view diagram schematically illustrating internal structure of the printer 130. In FIG. 2, elements of the printer 130 are drawn as if seen through a front face of the casing. The printer 130 is an electrophotographic color printer, and includes a feeder section 10, an imaging section 20, a fixing section 30, and a discharge section 40. The sections 10, 20, 30, 40 cooperate to form an image on a sheet based on image data while conveying the sheet in the casing of the MFP 100.

The feeder section 10 is a mechanical section of a paper feeder mounted to the printer 130, and makes use of conveyance rollers 12P, 12F, 12R, 13, 15F, 15R, 16X to separate sheets one by one from a sheet stack SHT stored in/on the paper feed cassette 11 or the manual feed tray 16. The feeder section 10 further feeds a separated sheet SH1 to the imaging section 20 at a defined timing by using a timing roller 14. The paper feed cassette 11 and the manual feed tray 16 are of a so-called universal design, and can store a variety of sheet types. A stored sheet may be made of a material such as paper or resin, and may be of a type such as plain, high quality, color, or coated. Sheet size is continuously adjustable in both length and width, in ranges including business cards, bookmarks, tickets, postcards, envelopes, and photographs, in addition to standard sizes defined by Japanese Industrial Standards (JIS), such as A3 to A7, B4 to B7, for example. Sheets may be oriented in portrait or landscape orientations.

The imaging section 20 forms a toner image on a sheet SH2 conveyed from the feeder section 10. More specifically, four imaging units 21Y, 21M, 21C, 21K first charge surfaces of internal photosensitive drums 25Y, 25M, 25C, 25K, respectively, and expose them to laser light from an optical scanner 26. For each photosensitive drum, the laser light is modulated on the basis of single different color of image data, either yellow (Y), magenta (M), cyan (C), or black (K), thereby forming electrostatic latent images in one-to-one correspondence with the exposed surfaces of the photosensitive drums 25Y, 25M, 25C, 25K. Next, the imaging units 21Y, 21M, 21C, 21K develop the electrostatic latent images with toner of the same color as the image data modulating the laser light, i.e., Y, M, C, K, respectively. The resulting four monochromatic toner images are sequentially transferred from surfaces of the photosensitive drums 25Y, 25M, 25C, 25K to the same position on a surface of an intermediate transfer belt 23 by electric fields between primary transfer rollers 22Y, 22M, 22C, 22K and the photosensitive drums 25Y, 25M, 25C, 25K. Thus, a color toner image is formed on the position on the surface of the intermediate transfer belt 23. When the color toner image then passes through a nip between a drive roller 23R of the intermediate transfer belt 23 and a secondary transfer roller 24, the color toner image is transferred to the front surface of the sheet SH2 passing through the nip at the same time by an electric field between the drive roller 23R and the secondary transfer roller 24. The sheet SH2 is conveyed to the fixing section 30 by a conveying force of the drive roller 23R.

The fixing section 30 thermally fixes a toner image to the sheet SH2 conveyed from the imaging section 20. More specifically, when the sheet SH2 is passed through a nip between a fixing roller 31 and a pressure roller 32, the fixing roller 31 applies heat from a built-in heater to the front surface of the sheet SH2 and the pressure roller 32 applies pressure to the heated portion of the sheet SH2, pressing the heated portion against the fixing roller 31. Due to heat from the fixing roller 31 and pressure from the pressure roller 32, the toner image is fixed to the front surface of the sheet SH2. Subsequently, the fixing section 30 conveys the sheet SH2 out from an upper portion of the fixing section 30.

The discharge section 40 uses a discharge roller 43 to discharge a sheet SH3 conveyed from the fixing section 30 from a discharge port 42 onto the discharge tray 44.

[Paper Feed Cassette Structure]

FIG. 3A is a perspective view diagram illustrating appearance of the paper feed cassette 11. The paper feed cassette 11 includes a body 210 and a tray 220.

The body 210 is a casing having the shape of a rectangular solid that is open at a top portion thereof. A front face 211 of the body 210 (a portion in a positive direction along the X axis in FIG. 3A) forms a part of a front face of the printer 130 and includes a handle 212 on an outer surface. Side surfaces 213, 214 of the body 210 extend in a direction of insertion and extraction of the paper feed cassette 11 (X axis direction in FIG. 3A), and a top end of one side 213 (in a positive direction along the Y axis in FIG. 3A) includes the pickup roller 12P. A rotary shaft of the pickup roller 12P extends in the direction of insertion and extraction of the paper feed cassette 11 (X axis direction), and both ends thereof are supported by an upper end of the body 210 so as to be rotatable. When the paper feed cassette 11 is accommodated in the casing of the printer 130, as illustrated in FIG. 2, the pickup roller 12P faces the nip between a paper feed roller 12F and a separation roller 12R.

The tray 220 is a substantially rectangular thin plate member that, along a lower surface 216 of the body 210, extends in a paper feed direction, i.e., a horizontal direction (Y axis direction) perpendicular to the insertion/extraction direction of the paper feed cassette 11 (X axis direction), from a central portion of the lower surface 216 to below the pickup roller 12P. At the central portion of the lower surface 216, an edge of the tray 220 is supported such that the tray 220 can swing about the edge. According to this swing, a slope angle of the tray 220 in the paper feed direction (Y axis direction) is variable. As indicated by a two-dot dash outline in FIG. 3A, a sheet stack SHT can be stacked on the tray 220. Due to the slope of the tray 220, the sheet stack SHT is accommodated in the paper feed cassette 11 such that one side nearest the pickup roller 12P, i.e., the leading end of the sheet stack SHT, is lifted up. In particular, the leading end of a sheet topmost in the sheet stack SHT is pressed against the outer circumferential surface of the pickup roller 12P.

FIG. 3B is a schematic diagram illustrating structure of the push-up mechanism 240 relative to the tray 220. In FIG. 3B, the body 210 of the paper feed cassette 11 is simplified (deformed) into a rectangular cuboid, and constituent elements 244, 245 of the push-up mechanism 240 are exaggerated. In FIG. 3A, the constituent elements 244, 245 are not indicated, but are embedded in the lower surface 216 of the body 210. The push-up mechanism 240 is a mechanism that changes a slope angle of the tray 220, and includes a push-up shaft 244 and a push-up plate 245. The push-up shaft 244 is a rod-like member extending above the lower surface 216 of the body 210 in the insertion/extraction direction (X axis direction), and both ends are supported by the body 210 to be rotatable. The push-up shaft 244 rotates when one end thereof receives a driving torque from an actuator such as a motor (not illustrated). The other end of the push-up shaft 244 supports the push-up plate 245. The push-up plate 245 is a plate-shaped member having a smaller area than the tray 220, and is disposed so as to be swingable about the push-up shaft 244 between an end portion of the push-up shaft 244 and the tray 220. When the slope angle of the push-up plate 245 is increased by rotation of the push-up shaft 244, a top end of the push-up plate 245 pushes up the tray 220 from below. Thus, the leading end of the sheet stack SHT stacked on the tray 220 is pressed against the outer circumferential surface of the pickup roller 12P.

According to rotation of the pickup roller 12P and the conveying force thereof, a topmost sheet SH1 of the sheet stack SHT goes up the slope of the tray 220 and is fed out from a top end of the side surface 213 of the body 210 to a nip between the paper feed roller 12F and the separation roller 12R (see FIG. 2). The paper feed roller 12F applies a conveying force to a front surface of the sheet SH1 that reaches said nip, and the separation roller 12R applies a conveying force to a back surface of the sheet SH1 in the opposite direction to the direction in which the sheet SH1 is conveyed (conveyance direction). If a next sheet is not fed along with the sheet SH1, the conveying force of the paper feed roller 12F acts on the separation roller 12R through the sheet SH1, and therefore a load torque of the separation roller 12R exceeds a threshold value, starting an internal torque limiter thereof. Accordingly, the separation roller 12R is driven to rotate by the paper feed roller 12F. If the next sheet is fed along with the sheet SH1, the conveying force of the paper feed roller 12F is not transmitted to the separation roller 12R beyond the overlapping sheets due to a low coefficient of friction between the sheets. Accordingly, progress of the next sheet is prevented by the conveying force of the separation roller 12R and the next sheet is separated from the sheet SH1.

[Manual Feed Tray Structure]

FIG. 4A is a perspective diagram illustrating appearance of the manual feed tray 16, and FIG. 4B is an enlargement of an area around a central portion of an interior of a frame 161 of the manual feed tray 16. The manual feed tray 16 includes the frame 161, a movable tray 162, and a movable holder 163.

—Frame—

The frame 161 is a substantially rectangular frame made of a highly rigid material such as a sheet metal such as stainless steel (SUS), aluminum alloy, or the like, or a molded reinforced plastic. The frame 161 is fixed to a chassis (not illustrated) of the MFP 100, and one face of a side pillar 169 is fixed to a back side of a side face of the casing of the MFP 100 (see FIG. 1, FIG. 2). Thus, the frame 161 surrounds an inside of a paper feed port 17 in the side surface of the casing of the MFP 100.

—Movable Tray—

The movable tray 162 is a substantially rectangular thin plate member made of, for example, molded reinforced plastic. The movable tray 162 is disposed such that one edge thereof is parallel to a long edge of a rectangular inner circumference of the frame 161, and both ends of the one edge are pivotally connected to a bearing 16B of a lower portion of the frame 161. By swinging about the one edge, the movable tray 162 can be opened out vertically (see FIG. 1 and the two-dot dash outline in FIG. 4A). An outer face of the movable tray 162 in a closed position as illustrated in FIG. 1 forms a part of a side surface of the printer 130. The movable tray 162 in an open position as illustrated in FIG. 2 and FIG. 4A is capable of having a sheet SH4 stacked on an upward-facing inner face 164 thereof (see dot-dash line in FIG. 4A).

Inside the frame 161, a push-up plate 165 extends along one edge of the inner face 164 of the movable tray 162. The push-up plate 165 is substantially an elongated rectangular plate, and a long edge 166 thereof (also referred to as a fixed edge), farthest from the inside of the frame 161, is pivotally connected to an inner face of the movable tray 162. By swinging about the fixed edge 166 to change slope, the push-up plate 165 displaces a long edge 167 thereof (also referred to as a movable edge), closest to the inside of the frame 161, up and down. As illustrated in FIG. 4A, when the movable edge 167 is at a lowest position (also referred to as a retracted position), the slope of the push-up plate 165 is such that an edge closest to the frame 161 of the sheet SH4 stacked on the inner face 164 of the movable tray 162, i.e., the leading end of the sheet SH4, slides down towards the inside of the frame 161. As illustrated in FIG. 4B, when the movable edge 167 is at a highest position (also referred to as a pressure contact position), the slope of the push-up plate 165 is reversed with respect to the slope of the inner face 164 of the movable tray 162.

—Movable Holder—

The movable holder 163 is a substantially rectangular cuboid casing, and is molded plastic, for example. The movable holder 163 is pivotally connected to a lower face of a beam 168 of the frame 161 such that one edge of an upper face of the movable holder 163 is parallel to the beam 168. By swinging about the one edge, a portion of the movable holder 163 protruding above the inner face 164 of the movable tray 162 can be displaced up and down from the beam 168 of the frame 161. FIG. 4A illustrates a highest position (also referred to as a retracted position) of the portion of the movable holder 163, and FIG. 4B illustrates a lowest position (also referred to as a pressure contact position) of the portion of the movable holder 163. A range in which the movable holder 163 swings is inside of the side pillar 169 of the frame 161 when viewed from the front face side of the MFP 100 (from the positive direction of the X axis). Accordingly, the swing range does not interfere with a movement range of the movable tray 162 when opening and closing. Thus, a structure or mechanism is not required on the inner face 164 of the movable tray 162 for avoiding the movable holder 163 when closing the movable tray 162.

[Manual Feed Tray Paper Feed Mechanism]

FIG. 5A and FIG. 5B are perspective view diagrams of the movable holder 163 and the push-up plate 165 in their respective retracted positions. FIG. 6A and FIG. 6B are perspective view diagrams of the movable holder 163 and the push-up plate 165 in their respective pressure contact positions. In FIG. 5A and FIG. 6A, the beam 168 of the frame 161 is drawn as if it were transparent. In FIG. 5B and FIG. 6B, the beam 168 is omitted, and the movable holder 163 is drawn as if it were transparent. FIG. 7A and FIG. 7B are front view diagrams of the movable holder 163 and the push-up plate 165 in the retracted positions and the pressure contact positions, respectively. In all drawings, elements that are obvious to a person skilled in the art, including supporting members such as screws, are omitted for the purpose of clarifying elements important to the present disclosure. As illustrated in FIGS. 5A to 7B, a paper feed roller 15F, a drive shaft 15S, a separation roller 15R, a solenoid 15D, and a link lever 15L are disposed below the beam 168 of the frame 161, and an auxiliary roller 16X, a gear train 16G, and a weight 16W are accommodated in the movable holder 163.

—Paper Feed Roller—

The outer circumferential surface of the paper feed roller 15F is smoothly covered in a resin that has a high coefficient of friction with respect to the sheet and excellent wear resistance, such as ethylene propylene diene rubber (EPDM), silicone rubber, or the like. The paper feed roller 15F is supported to be rotatable about a central shaft thereof by a bearing member (not illustrated) attached to a lower face of the beam 168 of the frame 161. The paper feed roller 15F has an axial direction parallel to a width direction (X axis direction in the drawings) of the movable tray 162 and is positioned above a central portion of the movable tray 162 in the width direction. Both ends of the central shaft of the paper feed roller 15F pass through arm portions 16A extending from edges of side faces of the movable holder 163. Thus, the central shaft of the paper feed roller 15F supports the movable holder 163 such that the movable holder 163 can swing between the retracted position and the pressure contact position. Further, the outer circumferential surface of the paper feed roller 15F intersects with a locus fitted to motion of the movable edge 167 of the push-up plate 165 or an extension of the locus in the direction of the motion (hereinafter also referred to as track TRC). Accordingly, when the push-up plate 165 moves from the retracted position to the pressure contact position with the leading end of the sheet SH4 stacked on the inner face 164 of the movable tray 162 and slid down towards the inside of the frame 161, the leading end of the sheet SH4 is pressed against the outer circumferential surface of the paper feed roller 15F.

—Drive Shaft—

The drive shaft 15S is a rod made of a highly rigid metal such as iron or SUS, and extends under the beam 168 in the longitudinal direction thereof (X axis direction). One end of the drive shaft 15S is connected to the central shaft of the paper feed roller 15F and the other end is connected to a shaft of a paper feed motor (see FIG. 8A, FIG. 8B) disposed inside the side pillar 169 of the frame 161. The drive shaft 15S transmits torque output by the paper feed motor to the paper feed roller 15F, causing the paper feed roller 15F to rotate (in a clockwise direction in FIG. 7A, FIG. 7B). Friction force accompanying this rotation acts as a conveying force on the sheet SH4 pressed against the outer circumferential surface of the paper feed roller 15F, and the leading end of the sheet SH4 is moved to the nip NP between the paper feed roller 15F and the separation roller 15R (see FIG. 7B).

—Separation Roller—

The outer circumferential surface of the separation roller 15R, like the paper feed roller 15F, is smoothly covered in a resin that has a high coefficient of friction with respect to the sheet and excellent wear resistance, such as ethylene propylene diene rubber (EPDM), silicone rubber, or the like. The separation roller 15R is supported by a bearing member (not illustrated) attached to a lower face of the beam 168 such that the separation roller 15R is rotatable about a central shaft thereof. The separation roller 15R forms a nip NP with the paper feed roller 15F downstream in the conveyance direction from the track TRC of the movable edge 167 of the push-up plate 165 (see FIG. 7B). A torque limiter is built into the central shaft of the separation roller 15R. When the load torque received by the separation roller 15R from the paper feed roller 15F via the nip NP is equal to or less than a threshold value, rotation of the separation roller 15R driven by the paper feed roller 15F is prevented, and when the load torque exceeds the threshold value, rotation of the separation roller 15R driven by the paper feed roller 15F is allowed. According to the torque limiter, the separation roller 15R exerts a resistance force in a direction opposite the conveyance direction against a back surface of the sheet SH4 entering the nip NP due to the conveying force of the paper feed roller 15F. Normally, if a next sheet is not fed along with the sheet SH4, the conveying force of the paper feed roller 15F acts on the separation roller 15R through the sheet SH4, and therefore the load torque of the separation roller 15R exceeds the threshold value. Accordingly, the separation roller 15R is driven to rotate by the paper feed roller 15F. If the next sheet is fed along with the sheet SH4, the conveying force of the paper feed roller 15F is not transmitted to the separation roller 15R beyond the overlapping sheets due to a low coefficient of friction between the sheets. Accordingly, the separation roller 15R is not driven to rotate by the paper feed roller 15F, and therefore the next sheet is prevented from proceeding by friction force received from the outer circumferential surface of the separation roller 15R, and separated from the sheet SH4.

—Movable Holder Actuator—

A combination of the solenoid 15D and the link lever 15L constitutes an actuator that moves the movable holder 163 between the retracted position and the pressure contact position. The solenoid 15D is fixed to the beam 168 of the frame 161 and supports a rod-like movable core 15P (also referred to as a plunger) that is parallel to the longitudinal direction of the beam 168 (X axis direction). The solenoid 15D makes use of a combination of a built-in electromagnet and spring to cause reciprocal movement of the plunger 15P in the longitudinal direction (X axis direction). The link lever 15L is a lever that is supported by a lower face of the beam 168 to be swingable between a leading end of the plunger 15P and a side surface of the movable holder 163 and is, for example, molded plastic. A swing shaft 151 that is the fulcrum of the link lever 15L is pivotally connected to a lower face of the beam 168. An effort-side arm 152 of the link lever 15L is in contact with the leading end of the plunger 15P and a load-side arm 153 of the link lever 15L is positioned below a protrusion 16P from a side face of the movable holder 163.

FIG. 8A and FIG. 8B are side view diagrams of the plunger 15P of the solenoid 15D, the link lever 15L, and the protrusion 16P of the movable holder 163. In particular, FIG. 8A illustrates a state in which the solenoid 15D pushes out the plunger 15P, and FIG. 8B illustrates a state in which the solenoid 15D draws back the plunger 15P. When the solenoid 15D pushes out the plunger 15P, the effort-side arm 152 is pushed by the leading end, and therefore the link lever 15L rotates about the swing shaft 151 (counterclockwise direction in FIG. 8A) such that a tip of the load-side arm 153 is brought into contact with the protrusion 16P of the movable holder 163 from below. Drive torque accompanying a force FP received from the plunger 15P by the effort-side arm 152 is larger than load torque according to a weight WH of the movable holder 163 received by the tip of the effort-side arm 153, and therefore the tip pushes the movable holder 163 up from below. As a result, the movable holder 163 rotates about the central shaft of the paper feed roller 15F that passes through the arm portions 16A, and moves to the retracted position. On the other hand, as illustrated in FIG. 8B, when the solenoid 15D draws back the plunger 15P, the leading end thereof releases the effort-side arm 152, and therefore the link lever 15L cannot support the weight WH of the movable holder 163. Accordingly, the movable holder 163 swings under its own weight to move from the retracted position to the pressure contact position. The effort-side arm 153 is pushed down by the projection 16P of the movable holder 163 falling, and therefore the link lever 15L rotates about the swing shaft 151 (clockwise direction in FIG. 8B) and the load-side arm 152 is again brought into contact with the leading end of the plunger 15P of the solenoid 15D. Thus, the position of the movable holder 163 is switched between the retracted position and the pressure contact position in accordance with the pushing out and drawing back of the plunger 15P as the solenoid 15D is turned on and off.

—Paper Feed Auxiliary Mechanism in Movable Holder—

A combination of the auxiliary roller 16X, the gear train 16G, and the weight 16W constitutes an auxiliary mechanism for enhancing the reliability of the feeding of the sheet SH4 by the paper feed roller 15F.

The auxiliary roller 16X is a roller whose outer circumferential surface is covered with a soft resin having a high coefficient of friction with respect to sheets, such as a soft polyurethane foam, and is supported to be rotatable about a central shaft supported by a bearing member (not illustrated) attached to an inner face of the movable holder 163. The auxiliary roller 16X has an axial direction parallel to a width direction (X axis direction in the drawings) of the movable tray 162 and a center of the auxiliary roller 16X in the width direction matches a center of the paper feed roller 15F. As the movable holder 163 swings, the outer circumferential surface of the auxiliary roller 16X is displaced, upstream in the conveyance direction of the track TRC of the movable edge 167 of the push-up plate 165. When the movable holder 163 is in the pressure contact position, the outer circumferential surface of the auxiliary roller 16X intersects a movement range MVR of the sheet SH4 according to changes in the slope of the push-up plate 165. When the movable holder 163 is in the retracted position, the outer circumferential surface of the auxiliary roller 16X is positioned outside of the movement range MVR of the sheet SH4.

The auxiliary roller 16X has a sufficiently smaller diameter than the paper feed roller 15F. Thus, even if size of the movable holder 163 in the Y axis direction is limited to an extent that the swing range of the movable holder 163 does not interfere with the movement range of the movable tray 162, the auxiliary roller 16X can be accommodated therein. Although the auxiliary roller 16X has a small outer diameter, axial direction grooves are formed at equal intervals in a circumferential direction on the entire outer circumferential surface thereof, and therefore the outer circumferential surface has a high flexibility. When the movable holder 163 is in the pressure contact position and the push-up plate 165 moves from the retracted position to the pressure contact position while the leading end of the sheet SH4 is in position having slid down on the movable tray 162 towards the inside of the frame 161, the leading end of the sheet SH4 contacts the outer circumferential surface of the auxiliary roller 16X. At this time, the movable holder 163 is not fixed in the normal direction from the sheet SH4, unlike the paper feed roller 15F. Accordingly, a force pushing down on the sheet SH4 from the auxiliary roller 16X is weaker than a force pushing up from the push-up plate 165, and is limited to the weight of the movable holder 163. However, due to the high flexibility of the circumferential surface of the auxiliary roller 16X, the actual contact area with the sheet SH4 expands to increase the coefficient of friction with respect to the sheet SH4.

The gear train 16G includes a main gear GM coaxially connected to the center shaft of the paper feed roller 15F, an auxiliary gear GA coaxially connected to the central shaft of the auxiliary roller 16X, and an intermediate gear GI engaged with the main gear GM and the auxiliary gear GA. A portion of the drive torque transmitted to the center shaft of the paper feed roller 15F from the drive shaft 15S is transmitted to the center shaft of the auxiliary roller 16X via the three gears GM, GI, GA. As a result, the auxiliary roller 16X rotates and stops at the same timing and in the same direction (clockwise direction in FIG. 6B) as the paper feed roller 15F. In particular, the conveying force imparted by the auxiliary roller 16X to the sheet SH4 in contact with the outer circumferential surface of the auxiliary roller 16X is in the same direction as the conveying force imparted by the paper feed roller 15F to the sheet SH4.

The weight 16W is a material having a high specific gravity and may be, for example, a rod made of iron, and is incorporated above the auxiliary roller 16X. Thus, overall weight of the movable holder 163 is increased, and the conveying force of the auxiliary roller 16X with respect to the sheet SH4 is adjusted within an appropriate range. The appropriate range is set to maintain contact between the sheet SH4 and the outer circumferential surface of the paper feed roller 15F. More specifically, the auxiliary roller 16X is designed to have a weaker conveying force and smaller sheet feed amount than the paper feed roller 15F. In particular, an upper limit is set for the conveying force of the auxiliary roller 16X. Thus, if the leading end of the sheet SH4 is prevented from proceeding at the nip NP between the paper feed roller 15F and the separation roller 15R, the auxiliary roller 16X is designed to slip on the surface of the sheet SH4. Thus, even without a special drive control, the auxiliary roller 16X does not increase the risk of a jam at the nip NP between the paper feed roller 15F and the separation roller 15R, unlike a pickup roller set to have the same conveying force and sheet feed amount as a paper feed roller.

FIG. 8C is a graph illustrating a relationship between the conveying force of the auxiliary roller 16X and a number of sheets passed through the nip NP between the paper feed roller 15F and the separation roller 15R. The graph illustrates plots of measurement results of the conveying forces of three auxiliary rollers 16X taken while passing sheets through three mechanisms of the same type as the paper feed mechanism described above. Note that cleaning of the auxiliary rollers 16X was not performed during the paper feeding. In each of the auxiliary rollers 16X, an initial value of the conveying force was set to an intermediate value of about 2 N between a buckling threshold of 4.0 N and a slip threshold of about 0.3 N. The buckling threshold indicates an upper limit of strength of the conveying force of the auxiliary roller 16X. As long as the conveying force of the auxiliary roller 16X is weaker than the upper limit, if a jam preventing the advance of the leading end of a sheet occurs at the nip NP between the paper feed roller 15F and the separation roller 15R, the conveying force of the auxiliary roller 16X alone is insufficient to feed a succeeding portion of the sheet to the nip NP. Thus, a risk of buckling the sheet and thereby making the jam worse is suppressed. The slip threshold indicates an upper limit of strength of the conveying force that satisfies a condition that the auxiliary roller 16X slips without moving the sheet. As illustrated in FIG. 8C, in each of the paper feed mechanisms, as the number of sheets fed increases, the conveying force of the auxiliary roller 16X weakens and therefore remains sufficiently weaker than the buckling threshold value. This is because the coefficient of friction between the auxiliary roller 16X and the surface of the sheet decreases along with an increase in amount of paper dust or the like adhering to the surface of the auxiliary roller 16X. On the other hand, the conveying force of the auxiliary roller 16X is kept sufficiently stronger than the slip threshold value. Thus, even when the leading end of a sheet is inadvertently separate from the outer circumferential surface of the paper feed roller 15F, the auxiliary roller 16X can return the leading end of the sheet to a position in contact with the outer circumferential surface of the paper feed roller 15F. That is, the function of the auxiliary roller 16X of maintaining contact between sheets and the paper feed roller 15F without causing buckling of the sheets can be sustained for a sufficiently long time.

[Manual Feed Tray Push-Up Mechanism]

FIG. 9A, FIG. 9B, and FIG. 9C illustrate a mechanism mounted inside the side pillar 169 of the frame 161, where FIG. 9A is a perspective view diagram viewed at an angle from the front of the MFP 100, FIG. 9B is a perspective view diagram viewed at an angle from the back of the MFP 100, and FIG. 9C is a back view diagram of the MFP 100. With the aim of clarifying elements that are important to the present disclosure, the beam 168 and the side pillar 169 of the frame 161 are drawn as if they are transparent in FIGS. 9A, 9B, 9C. In all drawings, elements that are obvious to a person skilled in the art, including supporting members such as screws, are omitted. A clutch 15M, a gear train 16H, a shielding plate 16S, a light sensor 16T, a stepped ring 16R, and a flapper solenoid 16D are mounted on an inner side of the side pillar 169, and a cam 16C is attached to an outer face of the side pillar 169 facing an edge of the push-up plate 165. These elements constitute a push-up mechanism for moving the push-up plate 165 of the movable tray 162 up and down.

The clutch 15M, the gear train 16H, and the cam 16C function as an actuator for up and down movement of the push-up plate 165, making use of drive torque from, for example, a stepping motor or a brushless direct current (BLDC) motor (not illustrated; also referred to as paper feed motor) installed inside the casing of the MFP 100. The clutch 15M transmits drive torque from the paper feed motor to the drive shaft 15S or cuts off the drive torque from the drive shaft 15S. Thus, timing of rotation of the paper feed roller 15F is controlled. The gear train 16H includes a main gear HM coaxially connected to the clutch 15M, an auxiliary gear HA connected to an eccentric axis RX of the cam 16C, and an intermediate gear HI engaged with the main gear HM and the auxiliary gear HA. A portion of drive torque transmitted from the clutch 15M to the drive shaft 15S is transmitted to the cam 16C via the three gears HM, HI, HA. The cam 16C is a small piece including a smooth closed curve outer circumferential surface like a slightly squashed annular surface, and is, for example, made of molded plastic. The cam 16C includes the eccentric axis RX positioned away from a geometric center of the cam 16C. The eccentric axis RX passes through the side pillar 169 and is coaxially connected to the auxiliary gear HA, and the cam 16C rotates about the eccentric axis RX along with the auxiliary gear HA. The outer circumferential surface of the cam 16C contacts an upper end face of a wall 16L extending upwards from an edge of the push-up plate 165 and blocks a force of a spring (not illustrated) pushing up a lower face of the push-up plate 165 from below. When the cam 16C rotates about the eccentric axis RX, a distance from the eccentric axis RX to the wall 16L of the push-up plate 165 increases and decreases according to a rotation angle of the cam 16C, and therefore the push-up plate 165 swings about the fixed edge 166 due to the force from the spring acting on the lower face of the push-up plate 165, and the movable edge 167 is moved up and down.

The shielding plate 16S, the light sensor 16T, the stepped ring 16R, and the flapper solenoid 16D function as a stopper against up and down motion of the push-up plate 165. A combination of the shielding plate 16S and the light sensor 16T monitors the rotation angle of the cam 16C. The shielding plate 16S is, for example, a plastic fan-shaped member connected to the eccentric axis Rx on the other side of the auxiliary gear HA from the cam 16C. Thus, the shielding plate 16S rotates along with the cam 16C. The light sensor 16T is, for example, a transmission type, and includes a light emitter and a light receiver in two arms protruding in a U-shape. A track of the fan portion of the shielding plate 16S passes between the two arms, intersecting a ray of light from the light emitter to the light receiver. Accordingly, whether or not the fan portion of the shielding plate 16S is outside the gap between the arms of the light sensor 16T is detected according to whether or not infrared or visible light emitted from the light emitter is detected by the light receiver. The stepped ring 16R is, for example, an annular member made of plastic and is coaxially connected to the auxiliary gear HA on the other side of the auxiliary gear HA from the cam 16C. Thus, the stepped ring 16R rotates along with the auxiliary gear HA. Two protrusions 16E protrude radially from the outer circumferential surface of the stepped ring 16R. The protrusions 16E are on opposite sides of a center of the stepped ring 16R. The flapper solenoid 16D uses a combination of a built-in electromagnet and spring CSP to bend a movable piece 16F (an elongated plate; also referred to as a flapper) in a direction perpendicular to a surface of the elongated plate, which increases and decreases a distance from a tip of the elongated plate to the outer circumferential surface of the stepped ring 16R. The tip of the flapper 16F is bent towards the outer circumferential surface of the stepped ring 16R to form a pawl 16K. When the flapper solenoid 16D moves the tip of the flapper 16F closer to the outer circumferential surface of the stepped ring 16R, the pawl 16K of the flapper 16F catches one of the protrusions 16E of the stepped ring 16R and applies a braking torque to the rotation thereof. A torque limiter is built into the shaft of the auxiliary gear HA that cuts off drive torque from the clutch 15M according to the braking torque from the pawl 16K of the flapper 16F. Accordingly, the auxiliary gear HA stops, which stops the cam 16C and the shielding plate 16S. The positions of the protrusions 16E of the stepped ring 16R are designed so that the rotation angle of the cam 16C when stopped corresponds to the retracted position or the pressure contact position of the push-up plate 165. Further, position of the shielding plate 16S relative to the auxiliary gear HA is determined in order to accurately detect from the output signal of the optical sensor 16T whether or not the rotation angle of the cam 16C is a target value corresponding to the retracted position or the pressure contact position of the push-up plate 165. For example, when the rotation angle of the cam 16C is equal to the target value, a center in the rotational direction of the shielding plate 16S is positioned between the arms of the optical sensor 16T.

[Image Forming Device Electronic Control System]

FIG. 10 is a block diagram illustrating a structure of an electronic control system of the printer 130. In the electronic control system, in addition to the feeder section 10, the imaging section 20, the fixing section 30, and the discharge section 40, an operation section 50 and a main control section 60 are connected via a bus 90 to be able to communicate with each other.

The operation section 50 is mounted on the MFP 100 and is an interface with users and external electronic devices. The operation section 50 accepts a job processing request and image data to be printed, via a user operation or communication with an external electronic device, and transmits same to the main control section 60. The operation section 50 includes an operation panel 51 and an external interface (I/F) 52. The operation panel 51 displays a graphical user interface (GUI) screen on a display, detects a position touched by a user on the screen via a touch panel, or identifies a button pushed by the user according to the screen, and transmits to the main control section 60 information related to the detection or identification as operation information. In particular, when an input screen of a print job is displayed on the display, the operation panel 51 receives print conditions from the user such as size, type, orientation, and number of sheets to be printed, image quality, etc., and incorporates same into the operation information. The external I/F 52 reads image data to be printed directly from an external storage such as a hard disk drive (HDD), a universal serial bus (USB) memory via a USB port or memory card slot, or the like. The external I/F 52 further receives image data to be printed from another electronic device via a communication port connected to an external network via wired or wireless means.

The main control section 60 is an integrated circuit mounted on one printed circuit board built into the printer 130, and includes a central processing unit (CPU) 61, a random-access memory (RAM) 62, and a read-only memory (ROM) 63. The CPU 61 is a microprocessor (MPU/CPU), and executes a variety of firmware. The RAM 62 is a volatile semiconductor memory device such as dynamic random-access memory (DRAM) or static random-access memory (SRAM) that provides a work area for execution of firmware by the CPU 61 and stores image data for printing received by the operation section 50. The ROM 63 is a combination of a non-writable nonvolatile storage device and a rewritable nonvolatile storage device. The former stores firmware, and the latter includes an HDD or a semiconductor storage device such as an electrically erasable programmable read-only memory (EEPROM), a Flash memory, a solid-state drive (SSD), or the like, and provides a storage area for environment variables and the like to the CPU 61.

The main control section 60 controls sections 10, 20, 30, 40, 50 in the printer 130, based on the operation information from the operation section 50 and according to the firmware executed by the CPU 61. More specifically, the main control section 60 controls the operation section 50 to display an operation screen so as to receive user operations. According to the user operations, the main control section 60 determines an operation mode such as a running mode, a standby mode, a sleep mode, or the like, notifies the other sections 10, 20, 30, 40, 50 of the operation mode via a drive signal, and thereby causes execution of processing by the sections 10, 20, 30, 40, 50 according to the operation mode. For example, when the operation section 50 receives a print job, the main control section 60 first causes the operation section 50 to transfer the image data to be printed to the RAM 62. Next, the main control section 60 notifies each of the sections 10, 20, 30, 40, 50 of the running mode and designates values of parameters required for processing, according to the print conditions. For example, for the feeder section 10, a storage location of a sheet to be fed (the paper feed cassette 11 or the manual feed tray 16), a paper type, size, number of sheets, and feed timing are specified, for the imaging section 20, image data is provided, and for the fixing section 30, temperature of the fixing roller 31 is specified.

—Feeder Section Control System—

The feeder section 10, the imaging section 20, the fixing section 30, and the discharge section 40 each include an electronic circuit system that controls movable members thereof. The control systems include actuators 10A, 20A, 30A, 40A such as motors, solenoids, or the like, control circuits 10C, 20C, 30C, 40C, and drive circuits 10D, 20D, 30D, 40D, respectively. The control circuits 10C, 20C, 30C, 40C and drive circuits 10D, 20D, 30D, 40D control drive forces that the actuators 10A, 20A, 30A, 40A apply to the movable members. In the feeder section 10, the movable members include a conveyance roller group 12P, 12F, 12R, 13, 14, 15F, 15R, 16X, and the actuator 10A includes the paper feed motor, the clutch 15M, the solenoid 15D, and the flapper solenoid 16D. The control circuits 10C, 20C, 30C, 40C are electronic circuits such as MPUs/CPUs, application-specific integrated circuits (ASIC), or field-programmable gate arrays (FPGA), and set target values for actuator output (control values) according to parameter values specified by the main control section 60 to instruct the drive circuits 10D, 20D, 30D, 40D. For example, in a conveyance roller drive control, a target value of a voltage applied to a motor is specified based on a target value of sheet conveyance speed specified by the main control section 60 and an actual revolution speed fed back from the motor. Further, according to conveyance timing specified by the main control section 60, a timing of voltage application to the motor is specified. The drive circuits 10D, 20D, 30D, 40D are switching converters that maintain target values of output by adjusting power supplied to actuators by using power transistors such as field effect transistors (FET), insulated gate bipolar transistors (IGBT), or the like as switching elements.

FIG. 11 is an example timing chart for signals the control circuit of the paper feeder 10 transmits to the drive circuit. In this example, three sheets are continuously fed from a stack of sheets stacked on the manual feed tray 16.

In the standby mode before the start of printing, both the push-up plate 165 and the movable holder 163 are stationary in the retracted position. When instructed by the main control section 60 to continuously feed three sheets from the manual feed tray 16, the control circuit of the feeder section 10 checks for presence of sheets stacked on the manual feed tray 16, for example from a state of a sensor (not illustrated) such as a mechanical switch incorporated into the inner face 164 of the movable tray 162. If there is no abnormality, the control circuit starts preparing paper feeding. First, the control circuit causes the flapper solenoid 16D to release the pawl 16K from the one of the protrusions 16E of the stepped ring 16R then starts the paper feed motor at a sufficiently low speed. Thus, the cam 16C starts to rotate, and therefore the push-up plate 165 starts moving from the retracted position (see start time TO indicated in FIG. 11). When it is confirmed from an output signal of the optical sensor 16T that the cam 16C has made a half turn, the control circuit causes the flapper solenoid 16D to catch the pawl 16K on the next one of the protrusions 16E of the stepped ring 16R, causing the clutch 15M to cut off drive torque from the paper feed motor. Thus, the push-up plate 165 is stopped in the pressure contact position, in a state where the leading end of the sheet stacked thereon is pushed against the outer circumferential surface of the paper feed roller 15F. While the push-up plate 165 is moving, the paper feed roller 15F and the auxiliary roller 16X rotate due to the drive torque from the clutch 15M. However, rotation of the clutch 15M is sufficiently low, and therefore the paper feed roller 15F cannot apply a conveying force to the sheet sufficient to move the sheet. Further, the movable holder 163 is in the retracted position, and therefore the auxiliary roller 16X does not contact the sheet. Accordingly, the sheet does not move from the movable tray 162 at the start time TO. Next, the control circuit of the paper feeder 10 draws in the plunger 15P into the solenoid 15D (see time T1 in FIG. 11). Thus, the movable holder 163 moves from the retracted position to the pressure contact position so that the outer circumferential surface of the auxiliary roller 16X presses against the sheet SH4 on the push-up plate 165, which is already in the pressure contact position. Thus, paper feed preparation is completed, with both the push-up plate 165 and the movable holder 163 moved to their respective pressure contact positions.

At time T2 (>T1) in FIG. 11, the control circuit of the paper feeder 10 starts paper feeding. First, the control circuit activates the paper feed motor at a rotation speed corresponding to the sheet conveyance speed specified by the main control section 60. Thus, the paper feed roller 15F rotates at a speed corresponding to the sheet conveyance speed, and synchronized to this the auxiliary roller 16X rotates in the same direction as the paper feed roller 15F, and therefore the first sheet is fed out from the manual feed tray 16. The control circuit keeps driving the paper feed motor until time T3. A time (T3−T2) from time T2 to time T3 is at least equal to a time required for the leading end of the first sheet to move from the paper feed roller 15F to the timing roller 14. At time T3, the timing roller 14 is stopped, and therefore progress of the leading end of the first sheet is stopped at the timing roller 14 and the sheet stops after the sheet bends into a bent shape in the conveyance path between the timing roller 14 and the paper feed roller 15F. The time (T3−T2) from time T2 to time T3 is set such that the bend is of a desired size.

Subsequently, in response to an instruction from the main control section 60, the control circuit of the feeder section 10 starts to rotate the paper feed roller 15F and the auxiliary roller 16X along with the timing roller 14 (see time T4 in FIG. 11). Accordingly, at a timing when a toner image to be transferred enters the nip between the drive roller 23R of the intermediate transfer belt 23 and the secondary transfer roller 24, the first sheet is passed through the nip. At a time T5 at which a trailing end of the first sheet is expected to exit the nip between the paper feed roller 15F and the separation roller 15R, the control circuit causes the clutch 15M to cut off the drive torque from the paper feed motor, and therefore the paper feed roller 15F and the auxiliary roller 16X are stopped. At a time T6 at which the trailing end of the first sheet is expected to exit the timing roller 14, the control circuit stops the timing roller 14. Thus, feeding of the first sheet is completed.

The control circuit of the feeder section 10 repeats the paper feeding operation from time T2 to time T6 a number of times equal to the number of sheets to be fed, which is three times in FIG. 11. Thus, three sheets are continuously fed from the manual feed tray 16. At a time T7 at which the trailing end of the last sheet is expected to exit the nip between the paper feed roller 15F and the separation roller 15R, after the drive torque from the paper feed motor is cut off at the clutch 15M, the control circuit starts a paper feed ending process. First, the control circuit causes the solenoid 15D to push out the plunger 15P (see time T8 in FIG. 11). Thus, the movable holder 163 moves from the pressure contact position to the retracted position, moving the auxiliary roller 16X away from the push-up plate 165 that is still in the pressure contact position. Next, the control circuit 10C causes the flapper solenoid 16D to release the pawl 16K from the one of the protrusions 16E of the stepped ring 16R then causes the clutch 15M to rotate at a sufficiently low speed. Thus, the cam 16C starts to rotate, and therefore the push-up plate 165 starts moving from the pressure contact position (see time T9 in FIG. 11). When it is confirmed from an output signal of the optical sensor 16T that the cam 16C has made a half turn, the control circuit causes the pawl 16K of the flapper solenoid 16D to catch on the next one of the protrusions 16E of the stepped ring 16R, causing the clutch 15M to cut off drive torque from the paper feed motor. Thus, the push-up plate 165 moves away from the paper feed roller 15F to the retracted position. Thus, in a state in which both the push-up plate 165 and the movable holder 163 are moved to their respective retracted positions, a paper feed end process is completed.

[Merits of Embodiments]

In a paper feeder according to an embodiment of the present disclosure, that is, in the feeder 10 of the MFP 100, the auxiliary roller 16X, which is upstream in the conveyance direction of the track TRC of the push-up plate 165 of the manual feed tray 16, exerts a conveying force in the conveyance direction of the paper feed roller 15F on the sheet SH4 pushed up by the push-up plate 165. Thus, the leading end of the sheet SH4 reliably maintains contact with the outer circumferential surface of the paper feed roller 15F, and therefore reliably enters the nip NP between the paper feed roller 15F and the separation roller 15R. Strength of the conveying force of the auxiliary roller 16X is such that when the leading end of the sheet SH4 is erroneously separated from the outer circumferential surface of the paper feed roller 15F, the leading end is returned to a position where it contacts the outer circumferential surface of the paper feed roller 15F. Accordingly, the distance of the auxiliary roller 16X from the paper feed roller 15F may be smaller, and the auxiliary roller 16X may be smaller than the paper feed roller 15F, and therefore the movable holder 163 that accommodates the auxiliary roller 16X can be made smaller and have a swing range such that it does not interfere with the movement range of the movable tray 162 opening and closing. Thus, a structure or mechanism is not required on the inner face 164 of the movable tray 162 for avoiding the movable holder 163 when closing the movable tray 162. Thus, the paper feed mechanism of the manual feed tray 16 can improve the reliability of taking in sheets without hindering miniaturization and cost reduction due to the omission of a pickup roller.

[Modifications]

(A) The image forming device 100 illustrated in FIG. 1 is an MFP. The paper feeder according to at least one embodiment of the present disclosure can also be used in a sheet conveyance device such as an ADF, finisher, automatic sorter, or the like provided to a single function image forming device such as a printer, copier, facsimile machine, or the like, or an image reading apparatus such as a scanner. Further, the auxiliary roller 16X is not limited to use with a manual feed tray similar to the manual feed tray 16 described above, and can be applied in the paper feed cassette 11 instead of the pickup roller 15P, for example.

(B) In the paper feed mechanism illustrated in FIGS. 6A, 6B, 7A, 7B, the paper feed roller 15F forms a nip with the separation roller 15R. The paper feed roller 15F may form a nip with an elastic material pad. Further, a membrane-like or plate-like member having a high coefficient of friction with respect to sheets, such as artificial leather, may be attached as a double feed prevention member along an entire or central portion of the movable edge 167 of the push-up plate 165. When a plurality of sheets are stacked on the manual feed tray 16, a sheet immediately below a sheet fed out by the paper feed roller 15F is prevented from proceeding due to a frictional force with the double feed prevention member, preventing the double feed.

(C) In the paper feed mechanism illustrated in FIGS. 6A, 6B, 7A, 7B, the gear train 16G transmits a portion of drive torque from the drive shaft 15S to the center shaft of the auxiliary roller 16X. Instead of the gear train 16G, a belt may be used to transmit torque.

FIG. 12 is a cross-section diagram of a mechanism in a movable holder 173 that makes use of such a belt for torque transmission. In the movable holder 173, a belt 17B is suspended between a drive pulley coaxially connected to the center shaft of the paper feed roller 15F and a driven pulley coaxially connected to the center shaft of the auxiliary roller 16X. A portion of drive torque transmitted from the drive shaft 15S to the center shaft of the paper feed roller 15F is transmitted to the center shaft of the auxiliary roller 16X by the rotation of the belt 17B along with the rotation of the paper feed roller 15F. As a result, the auxiliary roller 16X rotates and stops at the same timing and in the same direction (clockwise direction in FIG. 12) as the paper feed roller 15F. Further, tension TNS of the belt 17B applies a torque in a direction of rotation to the movable holder 173 itself so as to push the movable holder 173 towards the push-up plate 165. This supplements pressure applied by the auxiliary roller 16X to the sheet, and therefore the weight 16W can be omitted or reduced in size.

(D) Regarding the push-up plate 165 of the movable tray 162 and the movable holder 163 illustrated in FIGS. 6A, 6B, 7A, 7B, switching between the retracted position and the pressure contact position occurs at the timings illustrated in FIG. 11. The timing is implemented by electronic control with respect to the solenoids 15D, 16D by control circuitry of the paper feeder 10. A paper feed mechanism of the manual feed tray 16 may be designed such that, for example, a mechanical timing control is implemented by which a portion of torque for swinging the push-up plate 165 is transmitted to the movable holder 163 by a torque transmission mechanism such as gears, a belt, or the like.

<Review>

The embodiment and modifications described above illustrate one aspect for solving the technical problems described under the heading [Description of the Related Art], and may be summarized as follows:

An aspect of the present disclosure is a paper feeder that feeds out a sheet from a stack of sheets stacked on a tray, the paper feeder including: a push-up mechanism, a paper feed roller, a separation member, and an auxiliary roller. The push-up mechanism pushes up an end portion of the tray below a leading end of the stack. The paper feed roller includes an outer circumferential surface that intersects (i) a locus fitted to motion of an edge of the end portion of the tray when the push-up mechanism pushes up the end portion or (ii) an extension of the locus in the direction of the motion, the paper feed roller applying a conveying force to a sheet that the push-up mechanism presses against the outer circumferential surface of the paper feed roller via the end portion of the tray in order to move the sheet in a conveyance direction. The separation member forms a nip with the paper feed roller downstream in the conveyance direction from the locus, the separation member applying a resistance force in a direction opposite the conveyance direction to the sheet entering the nip due to the conveying force of the paper feed roller. The auxiliary roller includes an outer circumferential surface upstream in the conveyance direction from the locus, the auxiliary roller applying a conveying force in the conveyance direction to the sheet that the push-up mechanism presses against the outer circumferential surface of the auxiliary roller via the end portion of the tray, thereby maintaining a state of contact between the sheet and the outer circumferential surface of the paper feed roller.

According to at least one embodiment of the paper feeder, the conveying force and a sheet feed amount of the auxiliary roller are designed to be less than the conveying force and a sheet feed amount of the paper feed roller, respectively.

According to at least one embodiment of the paper feeder, the conveying force of the auxiliary roller is designed with an upper limit such that, if the leading end of the sheet is prevented from proceeding at the nip between the paper feed roller and the separation member, the auxiliary roller slips on a surface of the sheet.

According to at least one embodiment of the paper feeder, the paper feeder further includes a support mechanism that moves the auxiliary roller between a pressure contact position where the outer circumferential surface of the auxiliary roller intersects a movable range of the sheet when the push-up mechanism pushes up the end portion of the tray and a retracted position where the outer circumferential surface of the auxiliary roller is positioned outside the movable range.

According to at least one embodiment of the paper feeder, the support mechanism maintains the auxiliary roller at the pressure contact position during rotation of the paper feed roller and moves the auxiliary roller to the retracted position when the paper feed roller stops.

According to at least one embodiment of the paper feeder, the support mechanism maintains the auxiliary roller at the pressure contact position while the push-up mechanism pushes up the end portion of the tray and moves the auxiliary roller to the retracted position when the push-up mechanism lowers the end portion of the tray.

According to at least one embodiment of the paper feeder, a magnitude of a component in the normal direction of the sheet of a force applied to the sheet by the outer circumferential surface of the auxiliary roller at the pressure contact position is determined by a total weight of the auxiliary roller and components of the support mechanism including a bearing of the auxiliary roller.

According to at least one embodiment of the paper feeder, the support mechanism includes an actuator and a link mechanism that moves the auxiliary roller by using output of the actuator.

According to at least one embodiment of the paper feeder, the auxiliary roller includes a torque transmission mechanism that transmits to the auxiliary roller a portion of drive torque acting on the paper feed roller to synchronize rotation of the auxiliary roller with rotation of the paper feed roller.

According to at least one embodiment of the paper feeder, the torque transmission mechanism includes a belt that is suspended between a shaft of the auxiliary roller and a shaft of the paper feed roller and rotates the auxiliary roller as the paper feed roller rotates.

According to at least one embodiment of the paper feeder, the separation member includes an elastic material pad that forms a nip with the paper feed roller.

According to at least one embodiment of the paper feeder, the separation member includes a separation roller with a torque limiter and forms a nip with the paper feed roller.

According to at least one embodiment of the paper feeder, the tray is a manual feed tray.

An aspect of the present disclosure is an image forming device including: a paper feeder that feeds out a sheet from a stack of sheets stacked on a tray; a conveyance section that conveys the sheet fed from the paper feeder; and a printer that forms an image on the sheet conveyed by the conveyance section, the paper feeder including: a push-up mechanism, a paper feed roller, a separation member, and an auxiliary roller. The push-up mechanism pushes up an end portion of the tray below a leading end of the stack. The paper feed roller includes an outer circumferential surface that intersects (i) a locus fitted to motion of an edge of the end portion of the tray when the push-up mechanism pushes up the end portion or (ii) an extension of the locus in the direction of the motion, the paper feed roller applying a conveying force to a sheet that the push-up mechanism presses against the outer circumferential surface of the paper feed roller via the end portion of the tray in order to move the sheet in a conveyance direction. The separation member forms a nip with the paper feed roller downstream in the conveyance direction from the locus, the separation member applying a resistance force in a direction opposite the conveyance direction to the sheet entering the nip due to the conveying force of the paper feed roller. The auxiliary roller includes an outer circumferential surface upstream in the conveyance direction from the locus, the auxiliary roller applying a conveying force in the conveyance direction to the sheet that the push-up mechanism presses against the outer circumferential surface of the auxiliary roller via the end portion of the tray, thereby maintaining a state of contact between the sheet and the outer circumferential surface of the paper feed roller.

As described above, the auxiliary roller is upstream in the conveyance direction from the locus fitted to motion of the edge of the end portion of the tray when the push-up mechanism pushes up the end portion, and the auxiliary roller applies a conveying force in the conveyance direction of the paper feed roller to a sheet pushed up by the end portion of the tray by the push-up mechanism. This reliably maintains a state of contact between the leading end of each sheet and the outer circumferential surface of the paper feed roller, and therefore the sheets reliably enter the nip between the paper feed roller and the separation member. Strength of the conveying force of the auxiliary roller is such that when the leading end of the sheet is erroneously separated from the outer circumferential surface of the paper feed roller, the leading end is returned to a position where it contacts the outer circumferential surface of the paper feed roller. Accordingly, the auxiliary roller may be disposed a short distance from the paper feed roller and may have a simple structure, unlike a pickup roller. Thus, the paper feeder can improve the reliability of taking in sheets without hindering miniaturization and cost reduction due to the omission of a pickup roller.

Although one or more embodiments of the present invention have been described and illustrated in detail, the disclosed embodiments are made for the purposes of illustration and example only and not limitation. The scope of the present invention should be interpreted by the terms of the appended claims 

What is claimed is:
 1. A paper feeder that feeds out a sheet from a stack of sheets stacked on a tray, the paper feeder comprising: a push-up mechanism that pushes up an end portion of the tray below a leading end of the stack; a paper feed roller including an outer circumferential surface that intersects (i) a locus fitted to motion of an edge of the end portion of the tray when the push-up mechanism pushes up the end portion or (ii) an extension of the locus in the direction of the motion, the paper feed roller applying a conveying force to a sheet that the push-up mechanism presses against the outer circumferential surface of the paper feed roller via the end portion of the tray in order to move the sheet in a conveyance direction; a separation member that forms a nip with the paper feed roller downstream in the conveyance direction from the locus, the separation member applying a resistance force in a direction opposite the conveyance direction to the sheet entering the nip due to the conveying force of the paper feed roller; and an auxiliary roller including an outer circumferential surface upstream in the conveyance direction from the locus, the auxiliary roller applying a conveying force in the conveyance direction to the sheet that the push-up mechanism presses against the outer circumferential surface of the auxiliary roller via the end portion of the tray, thereby maintaining a state of contact between the sheet and the outer circumferential surface of the paper feed roller.
 2. The paper feeder of claim 1, wherein the conveying force and a sheet feed amount of the auxiliary roller are designed to be less than the conveying force and a sheet feed amount of the paper feed roller, respectively.
 3. The paper feeder of claim 1, wherein the conveying force of the auxiliary roller is designed with an upper limit such that, if the leading end of the sheet is prevented from proceeding at the nip between the paper feed roller and the separation member, the auxiliary roller slips on a surface of the sheet.
 4. The paper feeder of claim 1, further comprising a support mechanism that moves the auxiliary roller between a pressure contact position where the outer circumferential surface of the auxiliary roller intersects a movable range of the sheet when the push-up mechanism pushes up the end portion of the tray and a retracted position where the outer circumferential surface of the auxiliary roller is positioned outside the movable range.
 5. The paper feeder of claim 4, wherein the support mechanism maintains the auxiliary roller at the pressure contact position during rotation of the paper feed roller and moves the auxiliary roller to the retracted position when the paper feed roller stops.
 6. The paper feeder of claim 4, wherein the support mechanism maintains the auxiliary roller at the pressure contact position while the push-up mechanism pushes up the end portion of the tray and moves the auxiliary roller to the retracted position when the push-up mechanism lowers the end portion of the tray.
 7. The paper feeder of claim 4, wherein a magnitude of a component in the normal direction of the sheet of a force applied to the sheet by the outer circumferential surface of the auxiliary roller at the pressure contact position is determined by a total weight of the auxiliary roller and components of the support mechanism including a bearing of the auxiliary roller.
 8. The paper feeder of claim 4, wherein the support mechanism includes an actuator and a link mechanism that moves the auxiliary roller by using output of the actuator.
 9. The paper feeder of claim 1, wherein the auxiliary roller includes a torque transmission mechanism that transmits to the auxiliary roller a portion of drive torque acting on the paper feed roller to synchronize rotation of the auxiliary roller with rotation of the paper feed roller.
 10. The paper feeder of claim 9, wherein the torque transmission mechanism includes a belt that is suspended between a shaft of the auxiliary roller and a shaft of the paper feed roller and rotates the auxiliary roller as the paper feed roller rotates.
 11. The paper feeder of claim 1, wherein the separation member includes an elastic material pad that forms a nip with the paper feed roller.
 12. The paper feeder of claim 1, wherein the separation member includes a separation roller with a torque limiter and forms a nip with the paper feed roller.
 13. The paper feeder of claim 1, wherein the tray is a manual feed tray.
 14. An image forming device comprising: a paper feeder that feeds out a sheet from a stack of sheets stacked on a tray; a conveyance section that conveys the sheet fed from the paper feeder; and a printer that forms an image on the sheet conveyed by the conveyance section, the paper feeder comprising: a push-up mechanism that pushes up an end portion of the tray below a leading end of the stack; a paper feed roller including an outer circumferential surface that intersects (i) a locus fitted to motion of an edge of the end portion of the tray when the push-up mechanism pushes up the end portion or (ii) an extension of the locus in the direction of the motion, the paper feed roller applying a conveying force to a sheet that the push-up mechanism presses against the outer circumferential surface of the paper feed roller via the end portion of the tray in order to move the sheet in a conveyance direction; a separation member that forms a nip with the paper feed roller downstream in the conveyance direction from the locus, the separation member applying a resistance force in a direction opposite the conveyance direction to the sheet entering the nip due to the conveying force of the paper feed roller; and an auxiliary roller including an outer circumferential surface upstream in the conveyance direction from the locus, the auxiliary roller applying a conveying force in the conveyance direction to the sheet that the push-up mechanism presses against the outer circumferential surface of the auxiliary roller via the end portion of the tray, thereby maintaining a state of contact between the sheet and the outer circumferential surface of the paper feed roller. 